The last time I sent in a short story my letter contained the title, word count, and my list of previous commercially published works on a separate page. While I'm sort of known in one genre, I could not trust that anyone one in this other genre knew the name.
Having read the slush pile, I usually skipped reading cover/query and went straight to the submission. The most I did was to skim to see the word count and genre, then right to page one. If the writing did not grab me, no cover/query would help. I found many of them far too long. No need to fill the page, a single short paragraph is plenty. Agents get 100s of subs every week and haven't the time to savor every word. They want to see if you have something they can fall in love with and sell.
I see a query as being just the letter, no submission attached. "I have this gonzo novel, (title) that's 79K words complete. I've sold stories to _____ and am seeking representation. (Don't call it a "fiction novel!") Fans of (names of other authors in same genre) might enjoy this one."
Make sure the book IS in the right genre and is genuinely comparable to other books the agent has sold. Don't drop in the name of any old bestselling writer just-because. They are on to that one.
A cover letter (for me) is short and sweet: "Here is the requested (genre) title and first few chapters, per your reply on (date). I hope you like them and thank you for your time."
I leave out biographical info unless it has a bearing on the story. (I lived 5 years in Sri Lanka, the setting of the book.) No astrological signs, no pet pics, and NO glitter or confetti in snail mails.
Above all, no threats. I kid you not, some wanker told an editor/agent that if she didn't buy the story then SHE would suffer the same fate as the main character. The editor/agent said, "Bring it on, I'll introduce you to my Desert Eagle .50 caliber. BTW, you're story is rejected."
Gotta love this business!